1. Field of the Invention
The present invention relates to a ceramic multilayer through type capacitor array, comprising at least two or more multilayer through type capacitors in a ceramic chip.
With rapid growth of various types of electronic devices and equipment, these devices and equipment are increasingly produced in miniaturized and lightweight design. In particular, miniaturization and lightweight design are being used in electronic devices and equipment of portable type such as camera-integrated video tape recorders, portable telephone sets, note type personal computers, palmtop computers, etc.
With the propagation of miniaturization and lightweight design of the electronic devices and equipment, electronic parts are also increasingly produced in miniaturized and lightweight designs. The means for mounting electronic parts are also changing from conventional means for inserting and soldering electronic parts and pins used in through-hole on conventional type printed circuit board to surface mounting technology (SMT) for mounting and soldering electronic parts on conductive patterns provided on printed circuit boards.
The electronic parts used in SMT are generally called surface mounting devices (SMD), and these include semi-conductor parts as well as capacitors, resistors, inductors, filters, etc. (Among them, small parts such as capacitors and resistors are called chips.)
Among ceramic chip parts, there are composite parts called capacitor arrays and resistor arrays where a plurality of circuit elements, e.g. capacitors, resistors, or inductors, are incorporated. A multilayer capacitor array, comprising a plurality of ceramic multilayer capacitors, is a typical example of multilayer array parts.
Japanese laid-open publications Nos. 55-80319, 57-206015 and 57-206016 disclose a multilayer through type capacitor array consisting of capacitors, each of which is a through type capacitor.
To explain the structure of a conventional type multilayer through type capacitor array, FIGS. 1a through 1k show a multilayer through type capacitor array, which comprises four dielectric layers where four multilayer through type capacitor elements are combined together.
This multilayer through type capacitor array comprises a first dielectric sheet 1, a second dielectric sheet 2, a third dielectric sheet 3, and a fourth dielectric sheet 4, each designed in rectangular form and laid in this order.
FIGS. 1b, 1d, 1f, and 1h represent cross-sectional views of the dielectric sheets of FIG. 1a, 1c, 1e, and 1g along the lines b--b, d--d, f--f, and h--h respectively.
On the first dielectric sheet 1, an internal electrode 5 made of conductive material, extended in longitudinal direction of the rectangle and reaching the two shorter sides of the rectangle, is provided as shown in FIGS. 1g and 1h. On the second dielectric sheet 2, four internal electrodes 6, made of conductive material, extended in lateral direction of the rectangle and reaching the two longer sides of the rectangle, are provided as shown in FIGS. 1e and 1f. On the third dielectric sheet 3, an internal electrode 7 made of conductive material, extended in longitudinal direction of the rectangle and reaching only the shorter sides (similar to the internal electrode 5 on the first dielectric sheet 1) is provided. On upper surface of the dielectric sheet 3, the dielectric sheet 4 shown in FIGS. 1a and 1b having no internal electrode is placed.
External configuration of the multilayer through type capacitor array with the above structure is shown in FIG. 1i, and a cross-sectional view along the line j--j is given in FIG. 1j.
On the internal electrodes 6, four terminal electrodes 8 are formed, which are extended partially on mounting surfaces, i.e. upper and lower surfaces, by means such as printing. This is done in order to connect each of the multilayer through type capacitors, constituting the multilayer through type capacitor array, to an external printed circuit pattern. On the internal electrodes 5 and 7, two terminal electrodes 9 are formed, which are extended partially on mounting surfaces, i.e. upper and lower surfaces, by means such as printing in order to connect each of the multilayer through type capacitors, constituting the multilayer through type capacitor array, to an external printed circuit pattern.
Electrical connection diagram of the multilayer through type capacitor array is shown in FIG. 1k.
The multilayer through type capacitor array with the above arrangement comprises four multilayer through type capacitors, which have internal conductors 6 as central conductors and internal conductors 5 and 7 sandwiching the internal conductors 6 as external conductors. The through type capacitor is used by grounding the external conductor. In the multilayer through type capacitor array, the internal conductors 5 and 7, serving as common external conductors, are grounded by the terminal electrode 9.
The common external conductors 5 and 7 have impedance components. Because these impedance components serve as common impedance for four through type capacitors, crosstalk occurs via these impedance components.
In the multilayer through type capacitor array with the above arrangement, the distance from the external conductor of the multilayer through type capacitor, which uses internal conductors arranged inside as a central conductor, to the terminal electrode is longer than the distance from external conductor of the multilayer through type capacitor, which uses internal conductors arranged outside as a central conductor, to the terminal electrode.
For this reason, the inductance component of the external conductor in the multilayer through type capacitor, which uses an internal conductor arranged inside as central conductor, is different from the inductance component of the external conductor in the multilayer through type capacitor, which uses an internal conductor arranged outside as central conductor, and this makes electrical characteristics of capacitor array non-uniform, although it should be uniform.
Further, the distance between the multilayer through type capacitors, which constitute the multilayer through type capacitor array, is small, and multilayer through type capacitor elements are separated only by dielectric substances. In addition, central conductors of the adjacent multilayer through type capacitor elements are not completely covered by external conductors. Thus, capacitive coupling often occurs between the adjacent multilayer through type capacitor elements.
Capacitive coupling, although undesirable, is tolerable when operating frequency of the circuit is low. However, in a circuit where the operating frequency is over several hundreds of MHz such as portable telephone sets, crosstalk can occur between signals which pass through the multilayer through type capacitors adjacent to each other, and this often leads to undesirable consequences such as a decrease of signal-to-noise ratio or malfunction of the device incorporating the multilayer through type capacitors in the worst case.
FIGS. 2a through 2k show a conventional multilayer through type capacitor array, which solves the problems of the multilayer through type capacitor array of FIGS. 1a through 1k such as the problem due to common impedance or the problem of non-uniform electrical characteristics.
In the multilayer through type capacitor array of FIGS. 1a through 1k, the terminal electrodes of the external conductor in each multilayer through type capacitor are used in common, while in the multilayer through type capacitor array of FIGS. 2a through 2k, a terminal electrode of external conductor is provided on each of the multilayer through type capacitors.
This multilayer through type capacitor array also comprises a first dielectric sheet 11, a second dielectric sheet 12, a third dielectric sheet 13, and a fourth dielectric sheet 14, each designed in rectangular form and laid in that order (similar to the multilayer through type capacitor array of FIGS. 1a to 1k).
FIGS. 2b, 2d, 2f and 2h each represents a cross-sectional view of the dielectric sheets 11, 12, 13 and 14 of 2a, 2c, 2e and 2g respectively along the lines b--b, d--d, f--f and h--h.
On the first dielectric sheet 11, three internal terminal electrodes 15 made of conductive material, extended in the lateral direction of the rectangle and reaching the two longer sides of the rectangle, and an internal electrode 18 integrated with internal electrodes 15, extended in lateral direction of the rectangle and reaching none of the sides of the rectangle, are provided as shown in FIGS. 2g and 2h. On the second dielectric sheet 12, four internal electrodes 16 made of conductive material, extended in lateral direction of the rectangle and reaching the two longer sides at which the positions do not correspond to the internal electrodes 15, are provided as shown in FIGS. 2e and 2f. On the third dielectric sheet 13, three internal terminal electrodes 17 made of conductive material, extended in lateral direction of the rectangle and reaching the two longer sides, and an internal electrode 19 integrated with the internal electrodes 17, extended in lateral direction of the rectangle and reaching none of the sides of the rectangle, are provided as shown in FIGS. 2c and 2d. On upper surface of the dielectric sheet 13, a dielectric sheet 14 having no internal electrodes as shown in FIGS. 2a and 2b is placed.
The external configuration of the multilayer through type capacitor array with the above arrangement is shown in FIG. 2i, and a cross-sectional view along the line j--j is given in FIG. 2j.
On the internal terminal electrodes 15 and the internal terminal electrodes 17, three terminal electrodes 21 are provided, which are extended partially on mounting surfaces, i.e. upper and lower surfaces, by means such as printing. This is done in order to connect each of the multilayer through type capacitors, constituting a multilayer through type capacitor array, to external printed circuit pattern. On the internal electrodes 16, four terminal electrodes 20 are provided, which are extended partially on mounting surfaces, i.e. upper and lower surfaces, by means such as printing. This is done in order to connect each of the multilayer through type capacitors, constituting a multilayer through type capacitor array, to an external printed circuit pattern.
In each of the multilayer through type capacitors, which constitute the multilayer through type capacitor array, the internal electrodes 16 are used as central conductors, and the internal electrodes 18 and 19 are used as external conductors to sandwich the internal electrodes 16. These internal electrodes 16 as well as the internal electrodes 18 and 19 constitute the multilayer through type capacitor.
In the multilayer through type capacitor array, each of the terminal electrodes 15 and 17 are provided to correspond to sparings between the internal electrodes 16, serving as central conductors. Because these internal terminal electrodes 15 and 17 are grounded, impedance components of the external conductors do not provide common impedance even when the external conductors 18 and 19 are integrated, and no crosstalk occurs via these impedance components.
Also, the distances between the external conductor and the internal terminal electrode in each capacitor, which constitutes the multilayer through type capacitor array, are equal. Therefore, in this multilayer through type capacitor, inductance component of the external conductor in the multilayer through type capacitor, which uses the internal conductor arranged inside as central conductor, is equal to inductance component of the external conductor in the multilayer through type capacitor, which uses the internal conductor arranged outside as central conductor. Thus, the problem which makes characteristics of the capacitors of the capacitor array non-uniform, does not occur.
However, because three terminal electrodes 21 connected to external electrodes are provided between four terminal electrodes 20 connected to central electrode, the structure of the terminal electrodes are complicated, and it is difficult to miniaturize the multilayer through type capacitor array. Also, there are difficulties in manufacturing and mounting because spacings between the terminal electrodes are small.
Because spacings between the multilayer through type capacitor elements provided inside are small, the multilayer through type capacitor elements are adjacent to each other via dielectric substances, and central conductors of the multilayer through type capacitor elements adjacent to each other are not completely covered with the external conductors. For this reason, serious problems, such as crosstalk due to capacitive coupling between the adjacent multilayer through type capacitor elements, decrease of signal-to-noise ratio, or malfunction of devices incorporating the multilayer through type capacitors are not solved.
An electrical connection diagram of the multilayer through type capacitor array is shown in FIG. 2k.